Exhaust electrode process for exhaust gas oxygen sensor

Abstract

A method of sputtering a palladium or palladium-platinum exhaust gas electrode onto a vitrified zirconia thimble for an electrochemical-type exhaust gas oxygen sensor. Porous high surface area films are deposited that have more consistent properties. A sputtering target is spaced about 3.0-4.5 cm from the thimble and more than 6 cm from the sputtering anode. A pressure of about 10-20 millitorr is used during sputtering at a DC power of about 13-22 watts/cm 2 of target area.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a method of sputtering an electrode of at least one metal selected from the group consisting of platinum and palladium onto a vitrified zirconia solid electrolyte body for an electrochemical-type exhaust gas oxygen sensor, the improvement wherein a target of at least one metal selected from the group consisting of platinum and palladium spaced at least about 3.0 cm from the body is used in the sputtering, the metal is sputtered at a pressure of about 10-20 millitorr, and a sputtering power of about 13-22 watts/cm 2  of target area is used, whereby the electrode is porous as deposited and has an apparent surface area at least double the geometric area of the zirconia surface on which it lies. 
     
     
       2. In a method of sputtering a palladium exhaust gas electrode onto a vitrified zirconia thimble for an electrochemical-type exhaust gas oxygen sensor, the improvement wherein a generally planar target consisting essentially of palladium is oriented normal to the axis of the zirconia thimble and spaced about 3.0-4.5 cm from a closed end on the thimble, the palladium is sputtered using an atmosphere having a pressure of approximately 10-20 millitorr and a DC power of about 13-22 watts/cm 2  of target area, whereby the palladium electrode is consistently and reproducibly porous as deposited and forms a sensor electrode having a generally symmetrical switching response time. 
     
     
       3. In a method of sputtering a palladium exhaust gas electrode onto a vitrified zirconia thimble for an electrochemical-type exhaust gas oxygen sensor, the improvement wherein the thimble is about 3-5 cm long, a target having a generally planar surface consisting essentially of palladium is oriented normal to the thimble axis and spaced about 3.5-4.0 cm from a closed end on the thimble, the palladium is DC magnetron sputtered in an argon atmosphere having a pressure of approximately 10-20 millitorr and a DC power of about 13-22 watts/cm 2  of target area and for a duration to produce an electrode thickness of about 1.0-1.5 micrometer on said end and about 0.65-1.0 micrometer on thimble side walls about 0.5 cm back from that end, whereby the palladium electrode is porous as deposited and has an apparent surface area as deposited at least double its geometric surface area.